|
PROLOG | NAME | SYNOPSIS | DESCRIPTION | OPTIONS | OPERANDS | STDIN | INPUT FILES | ENVIRONMENT VARIABLES | ASYNCHRONOUS EVENTS | STDOUT | STDERR | OUTPUT FILES | EXTENDED DESCRIPTION | EXIT STATUS | CONSEQUENCES OF ERRORS | APPLICATION USAGE | EXAMPLES | RATIONALE | FUTURE DIRECTIONS | SEE ALSO | COPYRIGHT |
PATHCHK(1P) POSIX Programmer's Manual PATHCHK(1P)
This manual page is part of the POSIX Programmer's Manual. The Linux
implementation of this interface may differ (consult the
corresponding Linux manual page for details of Linux behavior), or
the interface may not be implemented on Linux.
pathchk — check pathnames
pathchk [−p] [−P] pathname...
The pathchk utility shall check that one or more pathnames are valid
(that is, they could be used to access or create a file without
causing syntax errors) and portable (that is, no filename truncation
results). More extensive portability checks are provided by the −p
and −P options.
By default, the pathchk utility shall check each component of each
pathname operand based on the underlying file system. A diagnostic
shall be written for each pathname operand that:
* Is longer than {PATH_MAX} bytes (see Pathname Variable Values in
the Base Definitions volume of POSIX.1‐2008, limits.h(0p))
* Contains any component longer than {NAME_MAX} bytes in its
containing directory
* Contains any component in a directory that is not searchable
* Contains any byte sequence that is not valid in its containing
directory
The format of the diagnostic message is not specified, but shall
indicate the error detected and the corresponding pathname operand.
It shall not be considered an error if one or more components of a
pathname operand do not exist as long as a file matching the pathname
specified by the missing components could be created that does not
violate any of the checks specified above.
The pathchk utility shall conform to the Base Definitions volume of
POSIX.1‐2008, Section 12.2, Utility Syntax Guidelines.
The following option shall be supported:
−p Instead of performing checks based on the underlying file
system, write a diagnostic for each pathname operand that:
* Is longer than {_POSIX_PATH_MAX} bytes (see Minimum
Values in the Base Definitions volume of POSIX.1‐2008,
limits.h(0p))
* Contains any component longer than {_POSIX_NAME_MAX}
bytes
* Contains any character in any component that is not in
the portable filename character set
−P Write a diagnostic for each pathname operand that:
* Contains a component whose first character is the
<hyphen> character
* Is empty
The following operand shall be supported:
pathname A pathname to be checked.
Not used.
None.
The following environment variables shall affect the execution of
pathchk:
LANG Provide a default value for the internationalization
variables that are unset or null. (See the Base Definitions
volume of POSIX.1‐2008, Section 8.2, Internationalization
Variables the precedence of internationalization variables
used to determine the values of locale categories.)
LC_ALL If set to a non-empty string value, override the values of
all the other internationalization variables.
LC_CTYPE Determine the locale for the interpretation of sequences of
bytes of text data as characters (for example, single-byte
as opposed to multi-byte characters in arguments).
LC_MESSAGES
Determine the locale that should be used to affect the
format and contents of diagnostic messages written to
standard error.
NLSPATH Determine the location of message catalogs for the
processing of LC_MESSAGES.
Default.
Not used.
The standard error shall be used only for diagnostic messages.
None.
None.
The following exit values shall be returned:
0 All pathname operands passed all of the checks.
>0 An error occurred.
Default.
The following sections are informative.
The test utility can be used to determine whether a given pathname
names an existing file; it does not, however, give any indication of
whether or not any component of the pathname was truncated in a
directory where the _POSIX_NO_TRUNC feature is not in effect. The
pathchk utility does not check for file existence; it performs checks
to determine whether a pathname does exist or could be created with
no pathname component truncation.
The noclobber option in the shell (see the set(1p) special built-in)
can be used to atomically create a file. As with all file creation
semantics in the System Interfaces volume of POSIX.1‐2008, it
guarantees atomic creation, but still depends on applications to
agree on conventions and cooperate on the use of files after they
have been created.
To verify that a pathname meets the requirements of filename
portability, applications should use both the −p and −P options
together.
To verify that all pathnames in an imported data interchange archive
are legitimate and unambiguous on the current system:
# This example assumes that no pathnames in the archive
# contain <newline> characters.
pax −f archive | sed −e 's/[^[:alnum:]]/\\&/g' | xargs pathchk −−
if [ $? −eq 0 ]
then
pax −r −f archive
else
echo Investigate problems before importing files.
exit 1
fi
To verify that all files in the current directory hierarchy could be
moved to any system conforming to the System Interfaces volume of
POSIX.1‐2008 that also supports the pax utility:
find . −exec pathchk −p −P {} +
if [ $? −eq 0 ]
then
pax −w −f ../archive .
else
echo Portable archive cannot be created.
exit 1
fi
To verify that a user-supplied pathname names a readable file and
that the application can create a file extending the given path
without truncation and without overwriting any existing file:
case $− in
*C*) reset="";;
*) reset="set +C"
set −C;;
esac
test −r "$path" && pathchk "$path.out" &&
rm "$path.out" > "$path.out"
if [ $? −ne 0 ]; then
printf "%s: %s not found or %s.out fails \
creation checks.\n" $0 "$path$path"
$reset # Reset the noclobber option in case a trap
# on EXIT depends on it.
exit 1
fi
$reset
PROCESSING < "$path" > "$path.out"
The following assumptions are made in this example:
1. PROCESSING represents the code that is used by the application to
use $path once it is verified that $path.out works as intended.
2. The state of the noclobber option is unknown when this code is
invoked and should be set on exit to the state it was in when
this code was invoked. (The reset variable is used in this
example to restore the initial state.)
3. Note the usage of:
rm "$path.out" > "$path.out"
a. The pathchk command has already verified, at this point, that
$path.out is not truncated.
b. With the noclobber option set, the shell verifies that
$path.out does not already exist before invoking rm.
c. If the shell succeeded in creating $path.out, rm removes it
so that the application can create the file again in the
PROCESSING step.
d. If the PROCESSING step wants the file to exist already when
it is invoked, the:
rm "$path.out" > "$path.out"
should be replaced with:
> "$path.out"
which verifies that the file did not already exist, but
leaves $path.out in place for use by PROCESSING.
The pathchk utility was new for the ISO POSIX‐2:1993 standard. It,
along with the set −C(noclobber) option added to the shell, replaces
the mktemp, validfnam, and create utilities that appeared in early
proposals. All of these utilities were attempts to solve several
common problems:
* Verify the validity (for several different definitions of
``valid'') of a pathname supplied by a user, generated by an
application, or imported from an external source.
* Atomically create a file.
* Perform various string handling functions to generate a temporary
filename.
The create utility, included in an early proposal, provided checking
and atomic creation in a single invocation of the utility; these are
orthogonal issues and need not be grouped into a single utility. Note
that the noclobber option also provides a way of creating a lock for
process synchronization; since it provides an atomic create, there is
no race between a test for existence and the following creation if it
did not exist.
Having a function like tmpnam() in the ISO C standard is important in
many high-level languages. The shell programming language, however,
has built-in string manipulation facilities, making it very easy to
construct temporary filenames. The names needed obviously depend on
the application, but are frequently of a form similar to:
$TMPDIR/application_abbreviation$$.suffix
In cases where there is likely to be contention for a given suffix, a
simple shell for or while loop can be used with the shell noclobber
option to create a file without risk of collisions, as long as
applications trying to use the same filename name space are
cooperating on the use of files after they have been created.
For historical purposes, −p does not check for the use of the
<hyphen> character as the first character in a component of the
pathname, or for an empty pathname operand.
None.
Section 2.7, Redirection, set(1p), test(1p)
The Base Definitions volume of POSIX.1‐2008, Chapter 8, Environment
Variables, Section 12.2, Utility Syntax Guidelines, limits.h(0p)
Portions of this text are reprinted and reproduced in electronic form
from IEEE Std 1003.1, 2013 Edition, Standard for Information
Technology -- Portable Operating System Interface (POSIX), The Open
Group Base Specifications Issue 7, Copyright (C) 2013 by the
Institute of Electrical and Electronics Engineers, Inc and The Open
Group. (This is POSIX.1-2008 with the 2013 Technical Corrigendum 1
applied.) In the event of any discrepancy between this version and
the original IEEE and The Open Group Standard, the original IEEE and
The Open Group Standard is the referee document. The original
Standard can be obtained online at http://www.unix.org/online.html .
Any typographical or formatting errors that appear in this page are
most likely to have been introduced during the conversion of the
source files to man page format. To report such errors, see
https://www.kernel.org/doc/man-pages/reporting_bugs.html .
IEEE/The Open Group 2013 PATHCHK(1P)